Heat a griddle medium hot.
Using your hands, form the beef into a 1/4-inch-thick patty, trying not to press the patty too much or the meat becomes tough and the patty does not cook properly in the center. Brush some butter on both sides of the patty, season with salt and pepper and cook on the griddle for 2 to 3 minutes. Flip the burger, place the cheese on top and continue griddling for 2 to 3 minutes for medium rare.
Meanwhile, brush softened butter on both slices of the bun and place on the griddle until toasted.
To assemble, place the hamburger on the bottom slice of the bun, and the lettuce, tomato and pickle on top of the hamburger. Spread the LT Guacamole on the top bun and then put the sandwich together and serve.
Mash the ingredients together in a medium bowl.